A common clinical problem in obstetrics is prolonged or in some way dysfunctional labor. Slow progress or arrest of labor is documented in about 40-60% of all parturitions in Sweden. In developing countries maternal deaths due to labor arrest with heavy post partum bleedings are the most common reasons for maternal deaths. Slow progress of labor is the most common indication for emergency caesarian section, which in turn often results in a demand for elective caesarian section at the next pregnancy. Other complications of protracted labor generate increased fetal asphyxia resulting in long-term sequele.
The uterus is composed of two parts, the corpus and the cervix having different functions during pregnancy and parturition. The corpus uteri consist predominantly of smooth muscle bundles, the myometrium, embedded in extra cellular matrix, ECM, and the cervix consists mainly of ECM. The dominating components of the ECM are the collagens, but there are also proteoglycans albeit in a smaller quantity. Proteoglycans consist of a protein core to which one to a hundred polysaccharide chains, the glycosaminoglycans, are attached.
The coordination between the uterine contractions and the softening, or in other words ripening, and dilation of the cervix is crucial for a normal parturition. Incongruity between these processes leads to abnormal parturitions.
During pregnancy and labor both the cervix and the corpus are remodeled. A profound remodeling of the corpus results in an approximately seven-fold increase in volume. An insufficient uterine remodeling is related to a disturbed contractility. A normal dilation of the cervix opening from 1 to 10 cm during established labor implies a total reconstruction of the cervical connective tissue generated through a decrease of the concentration of collagen and proteoglycans and resulting in a soft and elastic cervix. Disturbances in the cervical ripening can, if the process starts too early, result in a pre-term delivery. Pre-term labor must be coordinated with a pre-term cervical ripening in order to give a premature delivery. On the other hand insufficient cervical ripening results in post-term pregnancy with high frequency of protracted labor and instrumental deliveries. Thus the cervical ripening and myometrial contractions are two processes, which must be coordinated to accomplish a normal delivery.
The physiology of both normal and protracted labor is still obscure. The hormonal control seems to include an inhibitory effect by progesterone and activation by increasing estrogen levels. Corticotrophin releasing hormone, prostaglandin and a changed estrogen/progesterone ratio has been suggested to be involved in the initiation of labor. Intravenous infusion of oxytocin, introduced in 1950, is still the dominating treatment of protracted labor and recently published investigations and review articles on slow progress of labor mainly present different treatment schedules of oxytocin administration. This treatment fails in many cases and results in an increasing number of operative deliveries. There have been few efforts to develop new drugs for labor augmentation despite a tremendous global problem of slow progress of labor.
Induction of labor in women with unfavorable cervices has been performed by local application of prostaglandin E2 for about twenty years. In 15-20% of said cases cervical ripening and labor induction fail. Most prominent is arrest of labor.